Recently, a sensor net system have been developed which is consisted of sensor nodes and a sensor net server. In a sensor node, the status of a human being or a place (sensing data) is observed, and the observed sensing data is sent to the sensor net server. The sensor net server performs various processing based on the received sensing data.
In a sensor net system, sensor nodes are to be replaced regularly in order to calibrate sensor or to replace batteries. In addition, some sensor nodes are required to be migrated in order to temporarily measure a different environment and thus migrated sensor nodes are then required to be moved back to the original position.
With respect to the technology for replacing a terminal, JP-A No. 2005-159562 discloses a technology for replacing terminals which constitutes an IP network. The technology disclosed in JP-A No. 2005-159562, the relay device connected to a terminal stores a table indicating the correspondence between the assigned IP addresses to the terminals and the MAC addresses intrinsic to the terminals. After the replacement of a terminal, the relay device, upon reception of a request of establishing a communication link from a terminal connected thereto after the replacement, updates the table based on the IP address and MAC address included in the received request of establishing a communication link.